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Cisco Catalyst 6500 Virtual Switching System (VSS) design - Layer 2/3

Posted on 2011-09-25
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Cisco's Virtual Switching System (VSS) in the Catalyst 6500-series is a Layer 2 technology. The customer (currently w/ a non-VSS dual-core design), is routing at the edge - meaning, they have Cisco 3750 stacks in the closets configured for Layer 3 links (point-to-point /30 subnets between the closets and the core). They're dual-homed to each parent switch (again, non-VSS), so there's EIGRP load-balancing between the two equal-cost uplinks.  My questions:

Is it possible/feasible to deploy a unified VSS core design w/ L3 distribution links, or should VSS only be rolled out in environments w/ L2-only access closets?
Given that the customer already has L3 switching at the edge (w/ load-balancing across the dual-homed uplinks), does a VSS core really offer any benefit, performance/scalability-wise?
Thank you - reference links/docs are always appreciated.








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Question by:cfan73
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Don Johnston earned 2000 total points
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There are a couple schools of thought on this.

1) With layer 2 links, without VSS (and links to both 6500's that have been channeled), spanning tree will block all but one path. This makes VSS a no-brainer.

2) With layer 3 links, the load balancing is being handled by the routing algorithm. Which will be at least as good as the etherchannel algorithim.

3) Without VSS, there are two separate devices to be managed. With VSS, there is (effectively) one.

As for which is best, that depends on your definition of "best". :-)
 
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by:cfan73
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Thanks for the input, Don. It sounds as if the only benefit VSS would offer in a L3 routed environment would be the single IP management (much like a 3750 switch stack), which would be tough (for me) to justify wasting multiple 10-GE ports on each chassis just for this.  

Do you know if the same reasoning would apply to vPC (Virtual Port Channels) on the Nexus side, where there would be no reason to implement this in a routed L3 environment?


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by:Don Johnston
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>which would be tough (for me) to justify wasting multiple 10-GE ports on each chassis just for this.  

If you've already got the sup's in place and you're not using them, I don't see a downside to VSS.

>Do you know if the same reasoning would apply to vPC

Yes.
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